Structures with through vias passing through a substrate comprising a planar insulating layer between semiconductor layers

ABSTRACT

A through via contains a conductor ( 244, 262 ) passing through a substrate ( 140 ). The substrate can be SOI or some other substrate containing two semiconductor layers ( 140.1, 140.2 ) on opposite sides of an insulating layer ( 140 B). The through via includes two constituent vias ( 144.1, 144.2 ) formed from respective different sides of the substrate by processes stopping on the insulating layer ( 140 B). Due to the insulating layer acting as a stop layer, high control over the constituent vias&#39; depths is achieved. Each constituent via is shorter than the through via, so via formation is facilitated. The conductor is formed by separate depositions of conductive material into the constituent vias from each side of the substrate. From each side, the conductor is deposited to a shallower depth than the through-via depth, so the deposition is facilitated. Other embodiments are also provided.

BACKGROUND OF THE INVENTION

The present invention relates to integrated circuits, and moreparticularly to substrates having through vias possibly containingconductive features.

Through vias with conductive features are used to shorten conductivepaths between circuit elements in integrated-circuit packages. Forexample, FIG. 1 illustrates integrated circuit dies 110 attached to aprinted circuit board (PCB) 120 through an interposer 130. Theinterposer includes a substrate 140 with metalized through vias 144.Compared to a direct attachment of dies 110 to PCB 120, the interposercan redistribute the contact pads to reduce the package area (the areaof the entire structure). More particularly, dies 110 have contact pads110C attached to the interposer's contact pads 130C.1 by solder features150. The interposer has contact pads 130C.2 attached to contact pads120C of PCB 120 with other solder features 150. Many fabricationprocesses allow smaller critical dimensions in dies 110 than in PCB 120.Therefore, the die contacts 110C can be smaller, and spaced closer toeach other, than possible for PCB contacts 120C. Interposer 130 includesredistribution (rerouting) layers 154 with conductive lines 158connecting the interposer contacts 110C.1 to the metal in vias 144.Lines 158 allow the PCB contacts to be redistributed. For example, if adie's contacts 110C are positioned on the die's periphery rather thanbeing evenly distributed over the die's area, the corresponding PCBcontacts 120C can be evenly distributed over an area equal to the die'sarea. Therefore, the spacing between the PCB contacts can be enlargedwithout increasing the area. Further, some contacts 110C on the same ordifferent dies 110 may be designed for connection to the same input,e.g. the same signal or a power or ground voltage. Such contacts 110Cmay be connected to a single PCB contact 120C through lines 158,allowing the PCB contacts 120C to be fewer and occupy a smaller area.Thus, the area required for the die attachment is reduced.

Vias 144 should be narrow to reduce the package size. At the same time,the interposer's substrate 140 should be sufficiently thick to withstandthe mechanical and electrical stresses and meet the heat distributionrequirements during fabrication and operation. These two goals—narrowvias and a thick substrate—drive up the vias' aspect ratio. The highaspect ratio complicates both via formation and via filling with metal.In particular, it is difficult to provide reliable metallization,without voids or breaks, in high-aspect-ratio vias. Hence, the vias arewidened to undesirably increase the package area.

SUMMARY

This section summarizes some features of the invention. Other featuresmay be described in the subsequent sections. The invention is defined bythe appended claims, which are incorporated into this section byreference.

In some embodiments, the vias 144 are formed from opposite sides ofsubstrate 140. For example, the vias can be etched or drilled part waythrough the top of substrate 140 and part way through the bottom ofsubstrate 140. Also, metal (or another conductive material) can bedeposited into the vias part way through the top and part way throughthe bottom. In each processing operation such as deposition or etching,the via length subject to the processing operation is reduced,effectively reducing the aspect ratio subjected to processing.Therefore, the vias' aspect ratio can be doubled without changing theetch and deposition processes. See U.S. patent application Ser. No.13/042,186 filed Mar. 7, 2011 by the inventors of the presentapplication.

In some embodiments, substrate 140 is silicon-on-insulator (SOI). TheSOI substrate 140 includes two silicon layers on two sides of a “buried”insulator. The buried insulator acts as an etch stop during the two viaetches, i.e. from the top and the bottom. The via depths are thereforeuniform, even if different vias differ in shape, area, and/orfabrication methods forming the vias.

Silicon can be replaced by other semiconductor materials in the SOIsubstrate.

The invention is not limited to the features and advantages describedabove except as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vertical cross section of a semiconductor integratedpackage according to prior art.

FIGS. 2A-2J, 3A-3G show vertical cross sections of structures withthrough vias at different stages of fabrication according to someembodiments of the present invention.

FIGS. 4, 5 show top views of structures with through vias according tosome embodiments of the present invention.

DESCRIPTION OF SOME EMBODIMENTS

The embodiments described in this section illustrate but do not limitthe invention. The invention is defined by the appended claims.

FIGS. 2A-2J illustrate vertical cross sections of an SOI substrate 140at different stages of fabricating metalized vias 144 in someembodiments of the present invention. Substrate 140 can be used in aninterposer 130 as in FIG. 1, to connect dies 110 to PCB 120. Substrate140 can also be used to interconnect other structures attached to thetop and bottom of the substrate, e.g. dies attached to the top to diesattached to the bottom. The structures attached to the top and bottom ofsubstrate 140 may include other interposers. In other embodiments,substrate 140 is not an interposer but an integrated circuit notdirectly attached to any other integrated circuit. Vias 144 are used tointerconnect circuit elements at the top and bottom of such integratedcircuit, or to connect such elements to PCB 120 or to other dies orinterposers. Other uses of vias 144 may be possible.

As shown in FIG. 2A, substrate 140 consists of semiconductor layers140.1, 140.2 separated by buried insulating layer 140B. For the sake ofillustration, the example being described assumes that layers 140.1 and140.2 are monocrystalline silicon, and buried insulator 140B is silicondioxide (“buried oxide” or “BOX”). Other embodiments use othersemiconductor materials for layer 140.1 and/or 140.2 (e.g.gallium-arsenide, etc.) and other insulating materials for layer 140B(e.g. glass). The invention is not limited to particular materialsunless indicated to the contrary. Substrate 140 will be called a“wafer”. The wafer may have any shape (circular, rectangular, etc.).

Buried insulating layer 140B has planar top and bottom surfacescontacting, at all points, the adjacent planar surfaces of layers 140.1,140.2. In other embodiments, various features have been formed in layer140.1 and/or layer 140.2 to expose parts of insulator 140B.

Layers 140.1 and/or 140.2 have been thinned to their final thickness(e.g. 200 μm in some embodiments; the dimensions are not limiting unlessstated to the contrary). In this embodiment, layers 140.1, 140.2 havethe same final thickness to reduce the maximum depth of the to-be-formedvias 144. However, having the same final thickness is not necessary.

BOX 140B can be 1 μm thick, and other thickness values are possible.

A photoresist layer 210 is formed on layer 140.1. Resist 210 ispatterned to define the vias 144. Then vias are etched through layer140.1, and are shown as 144.1. The etch is selective to, and stops on,BOX 140B. Each via 144.1 will provide one segment of a via 144. Therecan be any number of vias 144. Some embodiments have thousands of suchvias. Other embodiments have a single via.

In the embodiment being described, vias 144.1 are formed by deepreactive ion etching (DRIE), and are shaped as circular cylinders with avertical sidewall of 65 μm diameter. Other processes (e.g. wet etch, orlaser drilling, with or without photoresist), and non-circular ornon-cylindrical shapes, with vertical or sloped sidewalls, can also beprovided. The invention is not limited to the shapes and processesmentioned unless stated to the contrary. Different vias 144.1 may havedifferent shapes and areas, and may or may not have vertical sidewalls.Different vias 144.1 may have differently sloped sidewalls in the samestructure, and may be formed by different processes. For example, somevias 144.1 may be formed by DRIE, and others by a wet etch. In the samevia, the sidewall may have different slopes on different sides and/or atdifferent depths on the same side. In some embodiments, some of the viaswill not be extended to through vias in the final structure.

Precise control of the via depth is easily achieved if the via etchesare selective to layer 140B. Precise control may or may not be importantdepending on the particular application, and may be especially importantif there are thousands of vias 144 scattered over the wafer. In some SOIembodiments, with layer 140.1 being silicon and with insulator 140Bbeing silicon dioxide, the silicon etch is performed by DRIE using theBosch process (time-multiplexed etching). The process involves repeatedetching steps (SF₆ plasma etch of silicon) alternating with passivationsteps to form passivation in the vias. Some embodiments use the etcherof type STS ASE HRM Multiplex from Surface Technology Systems (now SPPProcess Technology Systems) having an office in the United Kingdom. Insome of these embodiments, each etching step lasts 5 seconds, with theSF₆ flow rate of 200 ccm (cubic centimeters per minute), the coil powerof 1700 W, the platen power of 20 W, and the pressure of 30 mTorr. Eachpassivation step lasts 2 seconds, the C₄F₈ flow rate is 80 ccm, the coilpower is 1400 W, the platen power is zero, and the pressure is 15 mTorr.The etch selectivity to silicon dioxide 140B is about 150:1. Theresulting vias' sidewalls are generally vertical, but are locally uneven(undulating) as common for the Bosch process.

Photoresist 210 is stripped (see FIG. 2B-1), and photoresist 214 isformed on the “second” side of wafer 140 (the side of layer 140.2). Thewafer can be turned upside down for this purpose, i.e. with the secondside being on top. The wafer orientation in the drawings does not alwaysrepresent the actual orientation. Resist 214 is patterned to define vias144.2 through layer 140.1. In the embodiment shown, vias 144.2 are amirror image of vias 144.1. Therefore, the optical mask (not shown) usedto pattern the resist 214 can be a mirror image of the optical mask (notshown) used to pattern the resist 210 (FIG. 2A). Vias 144.2 can beformed by the same type of etch as vias 144.1 or by a different type ofetch. Vias 144.2 may or may not have the same respective shapes andsidewall slopes as the respective vias 144.1. The etch stops on buriedinsulator 140B.

Any shapes, dimensions, and sidewall angles are possible for differentvias in the same substrate, as illustrated in the example of FIG. 2B-2.Substrate 140 is at the same stage of fabrication as in FIG. 2B-1,except that the resist 214 has been removed. Vias 144.1 are shown as144.1A through 144.1C. Vias 144.2 are shown as 144.2A, 144.2B, and144.2D. Vias 144.1A, 144.2A may or may not be later joined to form athrough via (after the etch of buried oxide 140B described below). Vias144.1A, 144.2A are not perfectly aligned. Vias 144.1B, 144.2B mayprovide another through via. Vias 144.1B, 144.2B are also slightlymisaligned, and via 144.2B has a sloped sidewall while via 144.1B has avertical sidewall. Vias 144.1C, 144.2D will not be part of through vias.In some embodiments, via 144.1C is a trench whose sloped sidewall willprovide a mirror for a MEMS device. Via 144.1C was formed by a differenttype of etch (not by a perfectly anisotropic etch) than the vias 144.1Aand 144.1B. Vias 144.1A and 144.1B may also be formed by different typesof etches. Other variations are possible in vias' shapes, dimensions andfabrication processes.

In the examples of FIGS. 2A, 2B-1, 2B-2, described, substrate 140 wasthinned to its final thickness before the stage of FIG. 2A. In otherembodiments, one or both of silicon layers 140.1, 140.2 can be thinnedto their final thickness at a later stage. For example, layer 140.1 canbe thinned before the stage of FIG. 2A, and layer 140.2 can be thinnedafter formation of vias 144.1 before or after formation of vias 144.2.It may be desirable to thin each of layers 144.1, 144.2 to its finalthickness before the vias are etched through the layer, in order toreduce the etch depth. However, layer 144.1 and/or 144.2 can also bethinned after the via etch through the layer.

The subsequent fabrication steps will now be described on the example ofthe vias of FIG. 2B-1. As for FIG. 2B-2, the through-via fabricationprocess is similar. In either case, the through-via fabrication stepscan be combined with fabrication of other vias and other features in thesame structure.

As shown in FIG. 2C, insulator 218 is formed on the exposed siliconsurfaces (and possibly non-silicon surfaces) of substrate 140. Inparticular, insulator 218 covers the sidewalls of vias 144.1, 144.2. Insome embodiments, insulator 218 is silicon dioxide formed by thermaloxidation of silicon to an exemplary thickness of 0.5 μm. Otherinsulating materials, thickness values, and fabrication methods can alsobe used. Thermal oxidation provides good-quality silicon dioxide, butthe associated high temperature (about 1000° C.) may be undesirable iftemperature-sensitive elements (not shown) have been formed in or aboveor below substrate 140. Such elements may include transistorsource/drain regions or other doped regions, metal features, andpossibly other elements. Fabrication steps for such elements can beinterspersed with through-via fabrication steps being described.

Then metal is deposited into vias 144.1. For example (FIG. 2D), abarrier layer 226 (e.g. 250 nm thick titanium-tungsten) is deposited(e.g. by physical vapor deposition (PVD), possibly sputtering) on the“first” side of wafer 140, i.e. the side of layer 140.1. A seed layer230 is deposited on barrier layer 226 for electrodeposition. Forexample, the seed layer can be copper deposited to a 1 μm thickness byPVD, e.g. sputtering. (If desired, the seed layer thickness can beincreased by electrodeposition of additional copper.)

Higher quality (and in particular high thickness uniformity) of barrierand seed layers 226, 230 is achievable because vias 144.1 are only halfas deep as the thickness of substrate 140.

An electroplating mask 240 is then formed by depositing photoresist(e.g. dry film resist or some other type) over the first side ofsubstrate 140 and photolithographically patterning the resist to exposethe vias 144.1 and, possibly, areas immediately adjacent to the vias. Insome embodiments, the exposed areas are 85 μm in diameter around eachvia 144.1 into which the metal is to be electroplated, and each such via144.1 is at the center of the exposed area. In addition, mask 240exposes seed layer 230 at the edges (not shown) of substrate 140 forconnection to the cathode of a power supply (not shown) in thesubsequent electroplating step. Other areas (not shown) may also beexposed if electroplating is to be performed on those areas. Ifelectroplating is not to be performed into one or more of the vias 144.1or in any other areas, such vias and areas are left covered by mask 240.

Metal 244 (FIG. 2E), such as copper, is electroplated on the exposedsurfaces of seed layer 230 and, possibly, some adjacent areas. Thecopper fills the vias 144.1, and may protrude above the photoresist 240.

As shown in FIG. 2F, the first side of wafer 140 is planarized to exposethe seed layer 230 or, in alternate embodiments, to expose the insulator218. More particularly, in some embodiments, the wafer is first polishedby CMP (chemical mechanical polishing) that stops on resist 240. Thenthe resist is stripped, so that copper 244 forms upward protrusions atthe top. Then another CMP process polishes away the upward protrusions(bumps) of copper 244 to obtain a planar surface as shown in FIG. 2F.Seed layer 230 remains intact at the top, but in some embodiments theseed layer is removed outside of vias 144.1. Alternative processing,which also provides a planar top surface but removes the barrier/seedlayer from the wafer top to expose the insulator 218 outside of vias144.1, can be performed as described, for example, in the aforementionedU.S. patent application Ser. No. 13/042,186 filed by the inventors ofthe present application on Mar. 7, 2011 and incorporated herein byreference. The alternative processing begins like the processingdescribed above, i.e. copper 244 is polished by CMP, and then resist 240is removed leaving upward protrusions of copper 244. Then the exposedportions of barrier 226 and seed 230 are etched away (by dry and/or wetetching steps) outside of vias 144.1. Then an insulating layer (e.g.polyimide) is formed over the wafer. For example, the polyimide canlater insulate the silicon 140 from solder (not shown) when the wafer140 is soldered to PCB 120 (FIG. 1). After the polyimide deposition, aCMP process is applied to polish copper 244 and the polyimide down tothe level of the planar polyimide portions surrounding the vias 144.1.

Other processing is also possible, and a planar top surface is notrequired in some embodiments.

Then (see FIG. 2G showing the next processing stage for the case of FIG.2F) holes 144B are formed in buried insulator 140B to connect vias 144.1to respective vias 144.2 and thus form through vias 144 throughsubstrate 140. More particularly, an etch mask 246 is formed on thewafer's second side. In some embodiments, etch mask 246 is dry filmresist patterned to overhang the edges of each via 144.2 in which a hole144B will be made. The insulator 140B is then etched, e.g. by a dryvertical etch, to form the holes 144B. The etch exposes barrier layer226. Then barrier layer 226 is etched, with resist 246 and/or oxide 140Bas a mask, to expose copper seed 230. (Resist 246 may be removed beforethe etch of barrier 226.) An exemplary etch process etches bothinsulator 140B (silicon dioxide) and barrier layer 226(titanium-tungsten) by CF₄ in an etcher of type MULTIMODE® HF-8available from AXIS, Inc. having an office in California. In thisexample, the platen power is set to 500 W; the etch time is 40 minutes.

Then resist 246 is stripped (even it was not stripped before the etch ofbarrier 226). A protective layer 260 (FIG. 2H) is formed over thewafer's first side for protection in the subsequent electrodeposition ofcopper 262 into vias 144.2. In some embodiments, layer 260 is dry filmresist, but other materials can also be used. Layer 260 covers the wholewafer except for one or more areas (not shown) at the wafer periphery,to expose the seed layer 230 for connection to the cathode of a powersupply (not shown) for the electrodeposition of copper 262.

The electrodeposition is performed next. Copper 262 is electroplatedonto the exposed portions of seed layer 230 in holes 144B (marked inFIG. 2G). Copper 262 fills vias 144.2 and, possibly, extends to adjacentareas over the wafer's second side. Vias 144 become completely filledwith copper, the barrier layer, and insulator 218.

Protruding portions of copper 262 are removed on the second side, e.g.by CMP stopping on insulator 218, as shown in FIG. 2I.

In this embodiment, the sidewalls of vias 144.2 are not protected by abarrier layer. In other embodiments, a barrier layer (not shown, e.g.titanium tungsten) can be formed on the wafer's second side at asuitable stage, e.g. at the stage of FIG. 2F, before forming the resistmask 246 (FIG. 2G). In some such embodiments, when the mask 246 has beenformed, the barrier layer is etched in vias 144.2 to expose insulator140B, and then insulator 140B and barrier 226 are etched to expose theseed 230. Alternatively, after the barrier layer deposition on thesecond side, a seed layer can be formed on the second side on thebarrier layer. Then mask 246 can be formed, and the seed layer, thebarrier layer, and insulator 140B are etched to form openings 144B. Thebarrier layer 226 in vias 144.1 may or may not be etched since the seed230 does not have to be exposed in view of the seed layer on the secondside.

In another alternative processing of the second side, the barrier layer,with or without the seed layer, can be formed on the second side afterthe etch of openings 144B when the mask 246 has been removed.

In all such embodiments (with or without the barrier and seed layers onthe second side), the processing after electrodeposition of copper 262depends on the desired use of substrate 140. In the example of FIG. 2J,protective layer 260 is removed, and the first side is polished by CMPto the level of insulator 218. Then UBM (under ball metallization) 270is formed on copper 244, 262 by known techniques. Solder balls 150 areshown on the second side UBM features, but can also be formed on thefirst side UBM. The solder can be used to connect the metalized throughvias 144 to other structures (e.g. dies' or wafers' contact pads, bondwires, etc.).

Alternatively, an interposer 130 can be constructed as in FIG. 1.Rerouting layers 154 can be formed on the first and/or second side bydepositing and patterning insulating and conductive layers. Theconductive layers will provide lines 158 and contact pads 130C.1,130C.2. These contact pads can be attached to contact pads 110C, 120C bysolder, or conductive adhesive, or other means (e.g. bond wires).

Interposer 130 can be connected to other interposers and/or dies on bothsides (top and bottom). Substrate 140 can be diced into dies. Otherpassive and active circuit elements can be formed in the interposer.

Another fabrication process is illustrated starting with FIG. 3A. Thisand subsequent figures show vertical cross sections at different stagesof fabrication. The fabrication starts with the same type of substrate140 (e.g. an SOI substrate) as in FIG. 2A. This description will assumean SOI with silicon dioxide layer 140B, but other materials can be usedas in the processes of FIGS. 2A-2J.

Silicon layer 140.1 is thinned to its final thickness. Layer 140.2 isnot thinned at this stage. Therefore, the wafer is mechanicallystronger, more rigid, and has higher heat-dissipation capability.

Then vias 144.1 are formed in layer 140.1 as in FIG. 2A. (Thedescription immediately below will assume that the vias 144 will havethe same geometry as in FIG. 2B-1, but the geometry of FIG. 2B-2 is alsopossible.)

Next, insulator 218.1 (FIG. 3A) is formed on the exposed semiconductorsurfaces of layer 144.1, and possibly other surfaces. The same processescan be used as for insulator 218 of FIG. 2C. In some siliconembodiments, the insulator is silicon dioxide formed by thermaloxidation or CVD (chemical vapor deposition). If thermal oxidation isused, oxide 218.1 can also form on layer 140.2 as shown in FIG. 3A.

Then (FIG. 3B) the first side of the structure is processed as in FIGS.2D-2F. More particularly, barrier 226 and seed 230 are deposited, thenelectroplating mask 240 (FIG. 2D) is formed, then metal 244 iselectroplated (FIG. 2E), and then mask 240 and excess metal are removedto obtain a planar surface on the first side. The same materials andprocesses can be used as in FIGS. 2D-2F, and with the same variations(e.g. the top surface does not have to be planar, oxide 218.1 can beexposed on top, etc.).

Next (FIG. 3C), the wafer's second side is thinned, by mechanicalgrinding or another process. Insulator 218.1 becomes removed from thesecond side, and layer 140.2 is thinned to its final thickness.

Then (FIG. 3D) mask 214 (e.g. photoresist) is formed on the wafer'ssecond side, and vias 144.2 are etched, as described above in connectionwith FIG. 2B-1 or 2B-2.

Then (FIG. 3E) resist 214 is removed, and insulator 218.2 is formed onthe semiconductor and possibly non-semiconductor surfaces on the secondside of the wafer. If needed to avoid high-temperature damage to thefirst side elements (e.g. copper 244), then insulator 218.2 can beformed by a low-temperature process, e.g. by TEOS or some other type ofCVD for silicon dioxide, or by ALD (atomic layer deposition) of aluminumoxide.

The subsequent processing is similar to that of FIGS. 2G-2J, and thesame variations can be used as described for those figures. For example(FIG. 3F), holes 144B are formed at the bottom of vias 144.2 by a maskedetch using a mask 246 or by some other process essentially as describedabove in connection with FIG. 2G. In the embodiment of FIG. 3F,insulator 218.2 covers the bottoms of vias 144.2, and holes 144B passthrough insulator 218.2 and BOX 140B to expose barrier 226, and possiblyseed 230, and possibly copper 244.

The remaining processing can be as described above in connection withFIGS. 2H-2J. FIG. 3G shows an exemplary structure at the processingstage of FIG. 2J. Many variations are possible as described above forFIGS. 2H-2J. Still further processing can be as described above, to forminterposers or other types of devices.

Many other variations are possible for the processes and structuresdescribed above. For example, in some embodiments, metal 244, 262 doesnot fill the center portions of vias 144.1 and/or 144.2 but rather formsa thin film on the via sidewalls. Whether or not the metal fills thevias, the same metal layers can be deposited outside of vias (bysuitably patterning the mask layer 240 of FIG. 2D and mask layer 246 ofFIG. 2G for example) for use as interconnects, capacitor plates, or anyother suitable use. The process steps illustrated in FIGS. 2A-2J and3A-3G can be interspersed with other steps that form circuit elementsand other features in or on substrate 140.

The invention is not limited to the embodiments described above. Someembodiments provide a structure comprising:

a planar insulating layer (e.g. buried insulating layer 140B);

a first semiconductor layer (e.g. 140.1) overlying the planar insulatinglayer, the first semiconductor layer having a planar bottom surfacecontacting a top surface of the planar insulating layer;

a second semiconductor layer (e.g. 140.2) underlying the planarinsulating layer, the second semiconductor layer having a planar topsurface contacting a bottom surface of the planar insulating layer;

one or more through vias each of which passes through the planarinsulating layer and the first and second semiconductor layers, whereinin at least one through via the planar insulating layer protrudes intothe through via out of the first and second semiconductor layers. Forexample, in each of FIGS. 2J and 3G, in each through via 144 (formed bythe joining of a respective via 144.1 with a respective 144.2), buriedinsulating layer 140B protrudes into the through via out ofsemiconductor layers 140.1 and 140.2.

In some embodiments, in at least one trough via, the planar insulatinglayer protrudes into the through via out of the first and secondsemiconductor layers at each lateral position of the through via'ssidewall. For example, FIG. 4 shows the top view of the structure ofFIG. 2J or 3G around one circular through via 144, with all the featuresremoved except silicon layer 140.1, buried insulator 140B, and copper262. Buried insulator 140B is blocked from view by silicon layer 140.1except in through via 144. In the through via, buried insulator 140Bprotrudes into the through via out of silicon layer 140.1 at eachlateral position of the through via's sidewall, i.e. all around alongthe lateral boundary of the through via. Likewise, buried insulator 140Bprotrudes out of silicon layer 140.2 (not shown in FIG. 4) at eachlateral position of the through via's sidewall.

FIG. 5 shows a similar view for the case when the through via is atrench passing through the entire substrate 140. Buried insulator 140Bprotrudes into the through via on both sides of the trench, i.e. at eachlateral position of the through via's sidewall (the sidewall does notsurround the through via on all lateral sides, but the buried insulator140B protrudes wherever the sidewall is present).

In some embodiments, each of the one or more through vias comprises aconductor which provides a conductive path between the first and secondsemiconductor layers. For example, in FIG. 2J, the conductor may beinterpreted as copper 244, 262. Alternatively, the conductor can beinterpreted as including seed 230 and/or barrier 226. Non-copper andnon-metal conductive materials can also be used.

In some embodiments, at least one of the one or more through vias isfilled with the respective conductor or with a combination of therespective conductor (e.g. 244, 262, 230, 226 in FIG. 2J) and aninsulator (such as 218 in FIG. 2J) provided between the conductor andthe first semiconductor layer and/or between the conductor and thesecond semiconductor layer. An insulator can be omitted. Of note,semiconductor layers 140.1, 140.2 can be insulating layers (e.g. galliumarsenide).

In some embodiments, the first and second semiconductor layers have thesame thickness adjacent each through via. (A thickness of 200 μm wasnoted above, but this is not limiting.) However, the first and secondsemiconductor layers may also differ in thickness. For example, if Th1denotes the thickness of the first semiconductor layer at the side of athrough via, and Th2 denotes the thickness of the second semiconductorlayer at the same through via, then in some embodiments,

1/k*Th2≦Th1≦k*Th2

where k is a suitable value, e.g. 1.5, 2, 3, 10, or any other suitablevalue. Of note, each of Th1 and Th2 may have different values atdifferent vias in the same structure.

Some embodiments provide a manufacturing method comprising:

(1) obtaining a structure comprising:

a planar insulating layer (e.g. 140B) having a first planar surface anda second planar surface opposite to the first planar surface;

a first semiconductor layer (e.g. 140.1 or 140.2) having a planarsurface contacting the first planar surface of the planar insulatinglayer; and

a second semiconductor layer (e.g. 140.2 or 140.1) having a planarsurface contacting the second planar surface of the planar insulatinglayer;

(2) removing part of the first semiconductor layer to form one or morefirst vias (e.g. 144.1) through the first semiconductor layer, the oneor more first vias not passing through the planar insulating layer;

(3) removing part of the second semiconductor layer to form one or moresecond vias (e.g. 144.2) through the second semiconductor layer, the oneor more second vias not passing through the planar insulating layer;

(4) forming one or more through-holes (e.g. 144B) in the planarinsulating layer to join each second via with a respective first via toform a respective through via passing through the first and secondsemiconductor layers and the planar insulating layer; and

(5) forming a conductor in each through via, the conductor providing aconductive path in the through via between the first and secondsemiconductor layers.

In some embodiments, each through via comprises the respective one firstvia (e.g. 144.1) and the respective one second via (e.g. 144.2) whichare joined to form the through via;

the conductor in each through via comprises a first conductor portion(e.g. 244 and/or 226 and/or 230) present in the respective first via butnot in the respective second via, and comprises a second conductorportion (e.g. 262) present in the respective second via but not in therespective first via;

operation (5) comprises:

(5A) forming each first conductor portion without entirely forming atleast one second conductor portion (e.g. as in FIG. 2D or 2E or 2F);

(5B) before or after operation (5A), forming at least part of eachsecond conductor portion.

In some embodiments, each second conductor portion is entirely formed inoperation (5B), with no part of any second conductor portion beingformed in operation (5A).

In some embodiments (e.g. FIGS. 2F-2H), the operation (5A) is performedbefore (4), and the operation (5B) is performed after (4).

In some embodiments (e.g. FIG. 3B), the operation (5A) is performedbefore (3).

Other embodiments and variations are within the scope of the invention,as defined by the appended claims.

1. A structure comprising: a planar insulating layer; a firstsemiconductor layer overlying the planar insulating layer, the firstsemiconductor layer having a planar bottom surface contacting a topsurface of the planar insulating layer; a second semiconductor layerunderlying the planar insulating layer, the second semiconductor layerhaving a planar top surface contacting a bottom surface of the planarinsulating layer; one or more through vias each of which passes throughthe planar insulating layer and the first and second semiconductorlayers; wherein each through via's sidewall comprises: a firstsemiconductor portion provided by the first semiconductor layer; asecond semiconductor portion provided by the second semiconductor layer;and an insulator portion provided by the planar insulating layer;wherein in at least one through via the insulating portion protrudesinto the through via out of the first and second semiconductor portions.2. The structure of claim 1 wherein in at least one trough via, theplanar insulating layer protrudes into the through via out of the firstand second semiconductor layers at each lateral position of the throughvia's sidewall.
 3. The structure of claim 2 wherein each of the one ormore through vias comprises a conductor which provides a conductive pathbetween the first and second semiconductor layers.
 4. The structure ofclaim 3 wherein at least one of the one or more through vias is filledwith the respective conductor or with a combination of the respectiveconductor and an insulator provided between the conductor and the firstsemiconductor layer and/or between the conductor and the secondsemiconductor layer.
 5. The structure of claim 1 wherein the first andsecond semiconductor layers have the same thickness at each through via.6. The structure of claim 1 wherein for each through via,1/k*Th2≦Th1≦k*Th2 wherein Th1 is the thickness of the firstsemiconductor layer at the through via, Th2 is the thickness of thesecond semiconductor layer at the through via, and k is a value greaterthan 1 but less than or equal to
 10. 7. The method of claim 6 wherein kis less than or equal to
 5. 8. The method of claim 6 wherein k is lessthan or equal to
 3. 9. A manufacturing method comprising: (1) obtaininga structure comprising: a planar insulating layer having a first planarsurface and a second planar surface opposite to the first planarsurface; a first semiconductor layer having a planar surface contactingthe first planar surface of the planar insulating layer; and a secondsemiconductor layer having a planar surface contacting the second planarsurface of the planar insulating layer; (2) removing part of the firstsemiconductor layer to form one or more first vias through the firstsemiconductor layer, the one or more first vias not passing through theplanar insulating layer; (3) removing part of the second semiconductorlayer to form one or more second vias through the second semiconductorlayer, the one or more second vias not passing through the planarinsulating layer; (4) forming one or more through-holes in the planarinsulating layer to join each second via with a respective first via toform a respective through via passing through the first and secondsemiconductor layers and the planar insulating layer; and (5) forming aconductor in each through via, the conductor providing a conductive pathin the through via between the first and second semiconductor layers.10. The method of claim 9 wherein in each of operations (2) and (3), theremoving is selective to the planar insulating layer, the planarinsulating layer providing a stop for the removing.
 11. The method ofclaim 9 further comprising, before operation (5), forming an insulatorover a sidewall of each of the first and second vias.
 12. The method ofclaim 9 wherein: each through via comprises the respective one first viaand the respective one second via which are joined to form the throughvia; the conductor in each through via comprises a first conductorportion present in the respective first via but not in the respectivesecond via, and comprises a second conductor portion present in therespective second via but not in the respective first via; operation (5)comprises: (5A) forming each first conductor portion without entirelyforming at least one second conductor portion; (5B) before or afteroperation (5A), forming at least part of each second conductor portion.13. The method of claim 12 wherein each second conductor portion isentirely formed in operation (5B), with no part of any second conductorportion being formed in operation (5A).
 14. The method of claim 13wherein the operation (5A) is performed before (4), and the operation(5B) is performed after (4).
 15. The method of claim 13 wherein theoperation (5A) is performed before (3).
 16. The method of claim 12wherein the method further comprises: before operation (5A), forming aninsulator over a sidewall of each first via; before operation (5B),forming an insulator over a sidewall of each second via.
 17. The methodof claim 9 wherein the first and second semiconductor layers have thesame thickness at each through via.
 18. The structure of claim 9 whereinfor each pair of a first via and a second via joined into a through via,1/k*Th2≦Th1≦k*Th2 wherein Th1 is the thickness of the firstsemiconductor layer at the through via, Th2 is the thickness of thesecond semiconductor layer at the through via, and k is a value greaterthan 1 but less than or equal to
 10. 19. The method of claim 18 whereink is less than or equal to
 5. 20. The method of claim 18 wherein k isless than or equal to 3.